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Author Topic: TS-940 Blank LCD  (Read 7169 times)
AD6KA
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Posts: 2238




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« on: May 07, 2010, 01:52:30 AM »

The LCD display on my TS-940S has suddenly gone blank.
It IS lit up, so not a backlight problem,
No Graph, Clock, Memory or VFO freq display at all.

Anyone have an idea what would cause this?
I had a conversation on the air with a ham who said
that "there is a small battery for the memories
behind the LCD display". I notice that tapping on the top
of the rig above the LCD sometimes momentarrily
reveals very, very faint horizontal black lines on
the display, which make me think loose connection.

I have to replace the backlights on my S-Meter anyway,
so I thought I'd research this issue so I only have
to go behind the front panel once.

BTW: I have received conflicting advice as to the
part numbers/availability for the 940 **S-Meter lamps**. First I
heard that that they were no longer available.
I wrote Kenwood anyway and asked them.
Their replied with a part number and a link
to kenwood parts.com, which takes you
to "East Coast Transistor", where it is listed as "Discontinued".
Replied to that effect to a "dave" at Kenwood who
gave me the info and got a smartass reply.

Screw it, will use LED's or grain of wheat bulbs.

any help/advice appreciated 73, Ken  AD6KA
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KA1MDA
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Posts: 543




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« Reply #1 on: May 07, 2010, 08:23:34 PM »

I don't have a TS-940S, but according to the photo on Rigpix, the main display appears to be a Vacuum Fluorescent Display, not an LCD. It looks like there is an LCD next to it with a bar graph scale. Are you referring to the main (frequency) display or the other smaller display?  If it's the VF display, it's powered by a higher voltage (40+ volts) supplied by an inverter. If it went dead suddenly, check out the inverter circuit. Same type of technology was used to make the clocks light up on older VCR's. If it's the LCD, there is no inverter or high voltage drive.

Tom, KA1MDA
www.ka1mda.org
« Last Edit: May 07, 2010, 08:26:22 PM by Tom Rowinski » Logged
AD6KA
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Posts: 2238




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« Reply #2 on: May 07, 2010, 08:52:15 PM »

Hi Tom:
Thanks replying to my post.

Correct, it is the LCD graph display to the
immediate right of the vacuum fluorescent frequency
display, not that main display thank goodness.
(Which I like very much. Old technology, but easy on
the eyes and easy to read from any angle)
Thanks for the inverter voltage info.

I have a downloaded PDF service manual but it
is low resolution and difficult to read.

Looks like I'm gonna have to open this puppy
before I had planned to and have a look see.
Luckily everything is through hole parts.

tnx agn es 73, Ken AD6KA/5R8GQ
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KA1MDA
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Posts: 543




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« Reply #3 on: May 08, 2010, 01:17:26 AM »

I just had an idea- check the service manual and see if there is a contrast adjustment pot anywhere. I have seen some LCD's where turning the contrast adjust pot all the way down will make the display look dead.
could be a failed pot, solder joint, etc related to that.

Might want to check this link out- gives some basics on LCD operation:
http://www.tstonramp.com/~pddwebacc/lcd_cont_adj.htm

Tom, KA1MDA
« Last Edit: May 08, 2010, 01:21:14 AM by Tom Rowinski » Logged
KA5IPF
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Posts: 1039


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« Reply #4 on: May 08, 2010, 08:43:58 AM »

Tilt the front of the radio over. Looking down at the back of the sub-display in the lower left corner is a voltage regulator. It develops issues with the factory soldering job. Rework the solder on it and the choke inline with the output and that should fix it. Oh, make sure the choke hasn't opened up.  It goes without saying you have checked for power to the board, right? The bulbs get their power separately.

Clif
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AD6KA
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Posts: 2238




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« Reply #5 on: May 08, 2010, 10:12:12 AM »

Thanks for both posts, guys.

Now for even more vexation, the LCD started working
perfectly late last night. But then this AM is back to nothing.
So there is probably a bad joint, loose wire,
funky regulator,etc.

But I will check out all you guys recommended.
Time to go inside. I was going to wait until I had
some grain of wheat bulbs for the S-Meter but
will go with LED's instead.

Intermittent problmes are the worst to diagnose.

Thanks for all your replies....
73, Ken
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AD6KA
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Posts: 2238




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« Reply #6 on: May 08, 2010, 09:10:45 PM »

Problem Fixed!

On the bottom right of the LCD Board there
is a black plastic momentary switch. I just
puched it once and it reset all the LCD parameters.
VFO display, Clock, etc. That was it!

I decided to S-Meter lamps while I had her opened
up. I read many Net postings recommending Radio
Shack Part # 272-1092, a 12v 65ma mini grain of wheat bulb.
While I was there, I also noticed a very similar, slightly
larger 12v 25ma lamp with leads. The difference is that the
272-1092 bulb has very fine,bare leads, where the other 272-1141
ha longer insulated leads. I thought this would be easier
to install and I was right. Side by side brightness test
showed them identical. Neither is as pright as the factory bulbs, but
they aren't $7.19 each plus shipping, either! They're two for $1.49.

I am very happy to have my meter backlit again and the LCD display running.
Thanks for all your comments. Tom, I did check the contrast adjustment pot for the
LCD and made an adjustment there, thanks!

I plan to go back in with ultra high brightness LED's one
of these days, as I am not %100 happy with the meter
brightness, but I'm good for now.

OH FYI: The S-Meter lamp voltage on my rig read
at 13.3 volts. The two lamps are in parallel. One
of the "S-meter lamp replcaement" posts I read
said that the Kenwood factory standard should
be 8v. I couldn't find this in the Service Manual but
granted I didn't look very hard.

73, Ken  AD6KA
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KA5IPF
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« Reply #7 on: May 09, 2010, 08:47:43 AM »

The S-meter bulbs are 14v 80ma
The sub-display bulbs are 8v 50ma

Did you check the battery voltage. Usually when a reset has to be done the battery is marginal.

Clif
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AD6KA
Member

Posts: 2238




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« Reply #8 on: May 09, 2010, 12:15:39 PM »

The S-meter bulbs are 14v 80ma
The sub-display bulbs are 8v 50ma
Did you check the battery voltage. Usually when a reset has to be done the battery is marginal.
Clif
Hi Cliff:
Yes I did check the battery voltage.
(The one behind the LCD  sub display.)
It's reading 1.1vdc, so I think it needs to go.

Do you know the type, voltage, or Part Number?

My PDF copy of the Service Manual is so poor it's illegible,
and you can't even do a word or phrase searh with it
as you can with most PDF docs.

Thanks for the S-mtere & LCD display ma ratings.
Will be useful for when I switch to LED's, though they
don't draw near that current at 14v, is good info to
have on hand.

For S-Meter replacement lamps, if you are going to go
with grain if wheat bulbs over LED's, I highly recommend
Radio Shack 272-1141 over the usually suggested 272-1092.
They are much easier to work with. You have to snip a little
material over the soft plastic "boot" that holds it in place
but no big deal. Plus 2/$1.49 beats Kenwoods $7 each plus
shipping.


Thanks, any info about that sub display battery appreciated.
Hope it's a standard and not special order.....

73, Ken AD6KA
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AD6KA
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Posts: 2238




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« Reply #9 on: May 09, 2010, 12:54:52 PM »

Got the info.
There is avery good long treatise re TS-940 repair here:

 http://gatorradio.org/Manuals/Kenwood_TS-940S_Fixes_Reviews.pdf

The relevant internal battery issues, with photos,are dealt
with on pages 123-125.

It's a 3v coin type battery, No reason a similar off the shelf battery
won't work except that some original stock Kenwood internal batteries
of that era have metal tabs and leg pin wires on them
and are soldered to the board.

No reason they can't be replaced with a lithium CR series
3v battery, maybe with a higher ma rating....and a proper battery
holder to match.  If there was *room* in the rig I would
wire up a 3v AAA lithium battery holder and never worry
about it again for the life of the rig. I'm the original owner of this
radio, purchased at HRO Van Nuys in 1987.
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W9GB
Member

Posts: 2659




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« Reply #10 on: May 09, 2010, 04:17:37 PM »

IF you get your lithium coin cell from one of the Batteries Plus retail outlets --
they WILL spot solder the correct tabs to that battery (show them you old one).

They have that equipment because they rebuild the rechargeable battery sets for the Rechargeable shop tools (drills, saws, etc.) sold at Home Depot, Lowe's, Sears, etc.

WATCH the battery polarity -- BAD DAY if you hook it up backwards !

w9gb
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AD6KA
Member

Posts: 2238




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« Reply #11 on: May 09, 2010, 04:44:39 PM »

IF you get your lithium coin cell from one of the Batteries Plus retail outlets --
they WILL spot solder the correct tabs to that battery (show them you old one).
Hi Greg:
Thanks, that's terrific info, especially if I run into a battery in a REALLY bad place
and want to use the original configuration.

I removed the old Kenwood battery, legs, tabs and all,
and set it aside. I soldered wires to a plain CR2430 Lithium
cell from Frye's Electronics. I didn't bother with the old tabs because
I wanted to just *get it done*. I soldered wires directly to the battery
and then to the Digital A Board battery pads.
Everything works FB.

The CR2430 is rated 285 mah vs 540 mah for the 2450 that was in there
but makes no difference to me now that I see how easy it is to do.
So it lasts 10 years instead of 24 like the first one. <shrugs> I can live with that.
Interesting, the original 1980's Kenwood battery is labeled "MnO2".

Quote
WATCH the battery polarity -- BAD DAY if you hook it up backwards!
Thanks, I kinda figured that out when I got the board out and noticed
on the other side of the board direcly behind the battery is a 3/4" square
64 pin surface mount device. I said to myself:  "Self, I bet if you
mess up the polarity you WILL to replace that sucker, and it
WON'T be an available part".

Thanks to all who helped me with this. Ken AD6KA
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KB2CPW
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Posts: 304




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« Reply #12 on: May 10, 2010, 05:23:00 AM »


 Just so you know, soldering to the lithium battery itself seriously degrades its life expectancy. Regards, Richy N2ZD
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KA5IPF
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Posts: 1039


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« Reply #13 on: May 10, 2010, 07:50:18 AM »

When you solder to a lithium battery 1 thing happens and the other could.

The life is degraded, AND

it can explode. Not an old wives tale, do you need to talk to a ham who didn't believe me?

But then it's your eyeballs

Clif
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AD6KA
Member

Posts: 2238




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« Reply #14 on: May 10, 2010, 02:40:25 PM »

Thanks for the info.

We'll see how long this one lasts.
Only took 3 seconds to solder each side of the
battery, but like you say, always be careful.
If and when it happens again I *may* get the Kenwood
Part pre already soldered for install or have a baterry house
install the tabs.

Thanks for the safety info.
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